Mortise latchsets (more commonly referred to as “mortise locksets”) are a type of door latching assembly that fits into a rectangular cavity, called a “mortise,” that is cut into the side of a door. Mortise latchsets typically comprise a rectangular mortise latchset body that is inserted into the mortise, latchset trim (including inside and outside trim plates, doorknobs, and/or door handles), a strike plate or box keep that lines a cavity in the door jamb, and a keyed cylinder that operates the locking/unlocking function. A mortise latchset includes a typically self-latching main bolt or latchbolt, and optionally may also include a deadbolt and/or guardbolt. The mortise latchset body typically comprises a case assembly and cover that house the keyed cylinder and several levers, springs, and other moving parts used to bias, extend and/or retract the various bolts.
In a typical installation, it is preferred that only the outside door handle be access-controlled. The inside door handle should be free to operate the latch-retracting works inside the mortise latchset body. Accordingly, the latch-retracting works inside some latch assembly bodies includes two independently spindle-operable hubs, both of which are coupled to a latch-retracting works, but only one of which can be locked to prevent access.
Mortise latchsets are also frequently coupled with lever-type handles. A lever-type handle is a handle that, in the default position, extends preferentially to one side horizontally from and away from the handle's axis of rotation. In contrast to a typical rounded door knob, a lever-type handle has a center of gravity displaced a substantial radial distance from its axis, exerting torque on the corresponding hub and the latch-retracting works.
To compensate for the moment of the lever handle, some mortise latchsets provide a stiff spring assembly, housed inside the mortise latchset body, to bias the hub toward the default, non-latch-retracting position. However, to prevent the spring force from biasing the hub past the default, non-latch-retracting position, many latchsets include a stop means that prevents the hub from rotating past that position. Consequently, with such latchsets the lever can only be rotated down, but not also up, to retract the latch.
For example, U.S. Pat. No. 4,071,270 to Alexander illustrates a mortise lockset that includes a compression spring 90 pushing against a lower arm 70 of the outer hub 60. The compression spring 90 resists rotation of the outer hub 60 in a counterclockwise direction, and biases an attached outer lever handle to a horizontal, inactive position. To prevent the spring 90 from pushing the hub 60 clockwise past its inactive, non-latch retracting position, an upper arm 70 of the outer hub 60 engages an abutment 38 on the mortise case. Consequently, the lever 14 can only be rotated downward from its inactive, non-latch retracting position, in order to retract the latch.
As another example, U.S. Pat. No. 4,589,691 to Foshee et al. illustrates a mortise lockset with a pair of torsional hub springs 94 that bias corresponding bias arms 86a and 86b against corresponding camming surfaces 84 of the inner and outer hubs 46, 48. A stop pin 104 in close proximity to cam faces 70 of the hubs prevents the hubs from rotating past their inactive, non-latch retracting positions. Consequently, the door handle levers 16 and 18 can only be rotated downward from their inactive, non-latch retracting positions, to retract the latch.
Other mortise locksets include a spring-biased lever in the principle latch retractor assembly. One such configuration is illustrated in the prior art lockset illustrated in the background section of pending U.S. patent application Ser. No. 12/424,091, filed on Apr. 15, 2009, for a “Mortise Lock Assembly,” which is herein incorporated by reference. There, a torsion spring 44 biases lever 43 against cam faces of inner and outer hubs 31 and 32. This design enables either hub to be rotated clockwise or counterclockwise from a default position to retract the latch. The design also biases both inner and outer hubs toward the intermediate, non-latch-retracting position, when neither of the hubs 31 or 32 is operated. But when one of the hubs 31 or 32 is operated to retract the latch retractor assembly, the lever 43 no longer biases the non-operated hub toward its default position. While one remedy for this deficiency is to include biasing springs in each side of the trim, this prevents the mortise lock body from being used with pre-existing trim assemblies that cannot accommodate such biasing springs.
There is a need for an improved biasing mechanism for a dual-cam mortise latchset in which either an outside or an inside lever-type handle can rotate both clockwise and counterclockwise from a default, intermediate, inactive position to operate the latch retracting works. There is a need for the biasing mechanism to be housed inside the mortise latchset body and be operable to independently bias each operating cam and its corresponding lever-type handle to the default, inactive position, including during circumstances when one of the operating cams is rotated to operate the latch retracting works. There is also a need for the biasing mechanism to be sufficiently strong to bias conventional lever-type handles to a horizontal position without assistance from trim package springs.
Meeting these needs, however, is made even more challenging under certain design constraints. One example of such a design constraint is that the mortise latchset body be compatible with trim that attaches to the mortise latchset body through trim post holes located at the twelve and six o-clock positions above and below the operating cams. The location of the trim's posts would interfere with springs positioned like those shown in U.S. Pat. No. 4,071,270 to Alexander or U.S. Pat. No. 4,589,691 to Foshee et al.
Another example of a design constraint is that the mortise latchset be “reversibly-handed” or “field-reversible.” Mortise latchsets are often “handed,” that is, assembled for installation in either a left-hand door or a right-hand door, but not both. To convert a handed mortise latchset assembled for a left-hand installation to one adapted for right-hand installation, or vice-versa, it is often necessary to remove the cover from the case assembly, and then dismount, rotate or reverse, and remount several components (including the latchbolt, guardbolt, and spindle hubs) in the mortise latchset body. The background section of U.S. patent application Ser. No. 12/424,091 depicts an example of a prior art handed mortise latchset.
By contrast, a field-reversible mortise latchset is a reversibly-handed latchset in which it is not necessary to remove the cover from the case assembly in order to convert the lock from a left-hand installation to a right-hand installation. Field-reversible or reversibly-handed latchsets typically include additional hardware that would also interfere with conventional placements of biasing springs.
The above-mentioned design constraints are illustrated in connection with, or in contrast to, FIGS. 1 and 2, which illustrate an example of a prior-art field-reversible mortise lock and lock body assembly 10.
The present invention, however, can be characterized in many different ways, not all of which are limited by the above-mentioned needs or design constraints.